Travelling wire EDM apparatus

Abstract

A correction system for a travelling wire EDM machine cutting a workpiece by means of a travelling electrode wire stretched between two guide members and comprising a pair of servo motors for effecting displacement of the guide members relative to their respective support arms, such as to incline the electrode wire relative to the workpiece for providing the cut in the workpiece with an appropriate predetermined conicity or draft. One of the servo motors providing such displacement is, in addition, controlled such as to compensate for thermally-induced expansions or contractions of one of the support arm guide members relative to the other.

We claim: 
     
       1. In an apparatus for cutting by electrical discharges an electrode workpiece by means of a travelling electrode wire, said electrical discharges occurring in a machining zone between said electrode wire and said workpiece, said apparatus comprising a pair of electrode wire guide members mounted one on the end of a support arm and the other on the end of another support arm, said support arms being disposed parallel to each other on each side of the machining zone in the workpiece, and a pair of servo motors for displacing both said support arms in unison and said workpiece relative to each other along respective X- and Y-axes according to a predetermined path program, the improvement comprising a second pair of servo motors arranged one to displace one of said guide members in a first direction along the axis of its corresponding support arm and the other along a second direction perpendicular to the axis of its corresponding support arm such as to guide said wire with a predetermined inclination relative to said workpiece in the course of a cutting pass according to inclination information included in said path program, means for obtaining a pair of control signals from said program inclination information, means for controlling said one of said second pair of servo motors for displacing said one of said guide members relative to its corresponding support arm in said first direction as a function of one of said signals, and means for controlling the other of said second pair of servo motors for displacing the other of said guide members relative to its support arm in said second direction as a function of the other of said signals. 
     
     
       2. The improvement of claim 1 further comprising means for measuring the temperature of each of said support arms, means for determining the difference in temperature, and means for controlling said one of said second pair of servo motors for displacing said one of said guide members such as to compensate for difference in length of said support arms due to difference in temperature. 
     
     
       3. In an apparatus for cutting by electrical discharges an electrode workpiece by means of a travelling electrode wire, said apparatus comprising electrode wire guide members mounted each on the end of one of a pair of parallel support arms, one of said support arms being disposed above the workpiece and the other below the workpiece, a first pair of servo motors for displacing both said support arms in unison and said workpiece relative to each other along respective X- and Y-axes according to a predetermined path program, the improvement comprising means for measuring the temperature difference between said support arms and means for displacing one of said guide members along the axis of its support arm such as to compensate for difference in length of said support arms due to the difference in temperature.